This invention relates to multilamp photoflash units and, more particularly, to an improved photoflash unit having a circuit crossover provision for spaced apart conductor runs on a printed circuit board supporting an array for flashlamps within the unit housing.
Numerous multilamp arrangements with various types of sequencing circuits have been described in the prior art, particularly in the past few years. A currently marketed photoflash unit (described in U.S. Pat. Nos. 3,894,226 and 4,017,728 and referred to as flip flash) employs high voltage type lamps adapted to be ignited sequentially by successively applied high voltage firing pulses from a source such as a camera-shutter-actuated piezoelectric element. The flip flash unit comprises an elongated planar array of eight high voltage type flashlamps mounted on a printed circuit board with an array of respectively associated reflectors disposed therebetween. The lamps are arranged in two groups of four disposed on the upper and lower halves respectively of the rectangular-shaped circuit board. A set of terminal contacts at the lower end of the unit is provided for activation of the upper group of lamps, while a set of terminal contacts at the top of the unit is operatively associated with the lower groups of lamps. The application of successive high voltage pulses (e.g. 2,000 to 4,000 volts from, say, a piezoelectric source controlled by the shutter of a camera in which the array is inserted) to the terminal contact at the lower end of the unit causes the four lamps at the upper half of the array to be sequentially ignited. The array may then be turned end for end and again inserted into the camera in order to flash the remaining four lamps. In this manner one group of lamps (or half of the array) functions as a flash extender for the other group of lamps so that only the group of lamps relatively farther from the camera lens axis may be flashed. The purpose of such an arrangement is to position the "active" group of flashlamps farther above the camera lens in order to reduce the possibility of a "red-eye" effect that causes the pupils of a person's eyes to appear red or pink in flash pictures taken when the flashlamp is close to a camera lens.
The flip flash circuit board comprises an insulating sheet of plastic having a pattern of conductive circuit runs, including the terminal contacts, on one surface. The flashlamp lead-in wires are electrically connected to the circuit runs by means of eyelets secured to the circuit board and crimped to the lead-in wires. The circuitry on the board includes six printed, normally open, connect switches that chemically change from high to low resistance so as to become electrically conducting after exposure to the radiant energy from an ignited flashlamp operatively associated therewith. The purpose of these switches is to provide lamp sequencing and one-at-a-time flashing. The four lamps of each group are arranged in a parallel circuit, with three of the four lamps being connected in series with respective thermal connect switches. The circuitry on the board further includes a common circuit conductor run which is connected to one lead-in wire of each of the flashlamps in both groups and extends continuously from one end of the circuit board to the other between the common terminal contact at each end of the unit. Initially, only the first of the group of four lamps is connected directly to the high voltage pulse source. When this first lamp flashes, it causes its associated thermal connect switch (which is series connected with the next or second lamp) to become permanently conductive. Because of this action, the second lamp of the group of four is connected to the pulse source. This sequence of events is repeated until all four lamps have been flashed.
The overall construction of the flip flash unit comprises front and back plastic housing members with interlocking means for providing a unitary structure. The front housing member is a rectangular concavity, and the back housing is substantially flat. Sandwiched between the front and back housing members, in the order named, are the flashlamps, a unitary member, preferably of aluminum-coated plastic, shaped to provide the eight individual reflectors of the array, an insulating sheet, a printed circuit board, and an indicia sheet, which is provided with information trademarks and flash indicators located behind the representative lamps and which change color due to heat and/or light radiation from a flashing lamp, thus indicating at a glance which of the lamps have been flashed and not flashed. Each of the individual reflectors has a concave (generally parabolic) surface with the lamps being disposed within this concavity; the rear surface of the reflector has holes or slots to permit light and heat radiation to pass through for actuating circuit board switches and flash indicators. In order to provide electrostatic shielding for the lamps and circuitry, the reflector member is rendered electrically conductive by a reflective metalized coating thereon, and this coating is electrically connected to the common circuit conductor run on the printed circuit board. Further, a metal foil is laminated on the indicia sheet and also connected to this common conductor run of the circuit board.
U.S. Pat. No. 4,164,007 describes an improved multilamp photoflash unit which more efficiently utilizes a given housing volume and thereby reduces the cost of the unit per flashlamp contained therein. More specifically, a compact lamp arrangement is provided whereby additional lamps are contained in a given volume while maintaining light output performance requirements. In a particular embodiment described, ten lamps are provided in a housing having the same dimensions as the above-discussed eight-lamp flip flash unit. This greater compactness is provided by arranging the planar array of lamps in two parallel columns with the tubular envelopes horizontally disposed and with the lamps of one column staggered with respect to the others so that the bases are interdigitated. A pair of reflector panels are aligned with the two columns of lamps and are arranged to overlie the lamp lead-in wires and bases.
A copending application Ser. No. 072,251, assigned to the present assignee, describes a more compact cost-efficient photoflash unit construction comprising a linear array of electrically ignitable flashlamps mounted on a printed circuit board in the form of an elongated strip. The printed circuit strip is located within the longitudinal channel of an elongated housing member having reflective surfaces adjacent to the lamps. A light-transmitting cover panel is attached to the front of the housing member to enclose the flashlamps. The lamps have substantially tubular envelopes and are positioned extremely close to one another with their longitudinal axes substantially parallel to the surface of the printed circuit strip and in substantially coaxial alignment. Typically, the diameter of the lamps, the width of the printed circuit strip, and the width of the channel in the housing member are nearly equal. In order to provide protection against the red-eye effect, a double-ended linear array is described which operates in similar fashion to the aforementioned flip flash. In one specific embodiment, three lamps mounted in the upper half of the printed circuit strip are controlled by a pair of contact terminals at the lower end of the unit, while three lamps in the lower half of the unit are controlled by contact terminals at the top end of the unit. One of the contact terminals for controlling a group of lamps is connected in common to a lead-in wire of each of the lamps of the group, while the other contact is a "hot", or signal, terminal coupled through switching circuitry to the other lead-in wire of each of the lamps. Accordingly, in order to provide an interconnection between the signal terminals at each end of the unit and the respective switching circuitry controlled thereby on opposite halves of the printed circuit strip, respective signal conductor runs must be extended through the respectively inactive halves of the circuit strip. The interconnecting conductor runs from the common terminal contacts are disposed along the outer sides of the circuit-containing circuitry of the printed circuit board. More specifically, the common circuit conductor run on the bottom half of the circuit strip is located on opposite sides of the circuit strip. As a result, a crossover, or side-to-side connection of the common circuit run is required in order to connect the common terminal at one end of the printed circuit strip with the common circuit conductor run connected to lamp leads in the opposite half of the circuit strip. Such a problem is created by the severe crowding of the conductive paths of this extremely compact unit. The use of both sides of the circuit strip introduces undesirable cost, e.g. two circuit screening operations are needed as well as eyelets or other feed-through means. A minimum inter-run spacing of about 1.5 millimeters is necessary in order to prevent failure, i.e. promoting electrical sparkover from one run to another at the high voltages used (e.g. 2,000 volts or more).